Method of making alumina.



UNITED STATES PATENT orrron.

HERBERT 'r. KAI-Mus AND WALTER L. sAvELL, or KINGSTON, onra'nro, CANADA,

assrenons 'ro SAID KALMUS.

No Drawing.

Specification of Letters Patent.

METHOD or name ALUMINA.

, Patented Mar. 1'7, 1914.

To all whom it may concern:

Be it known that we, HERBERT T. KALMUS and WALTER L. SAVELL, citizensoffthe United States, both residing at Kingston, in the county ofFrontenac, Province of, Ontario, and Dominion of Canada, have inventedcertain new and useful Improvements in Methods of Making Alumina; and wedo hereby declare the following to be a .full, clear, and exactdescription of the invention, such as will enable others skilled in theart to which it appertains to make and use the same. I

The present invention relates to a process of obtaining alumina fromaluminous materials, and more particularly to a. process of obtainingalumina from nephelin syenite.

- The principal object of the 'invention is to reduce the cost 'ofproducing alumina suit- .aluminous materials hereinafter identified.

The process will be described-as it has been practised to obtain aluminafrom nephelin.

syenite. 7

The ore, nephelin syenite, is first ground to a fine powder. Thepulverized ore is then sulfited by a treatm'entiwith sulfur dioxid. Thesulfur dioxid treatment is carried out at ordinary room temperatures,and during this treatment, the mass is agitated to assist the chemicalreactions. The pulverized ore ,is put in a tank and covered with aboutthree times its weight of water and agitated,

at the same time passing in sulfur dioxid gas. There should bean excessof sulfur dioxid which may be had by passing an excess of sulfur dioxidgas into the Water during this treatment.- The nephelin syenite containssilica, soda, potassium oxid, aluminafoxids of iron and the like. Thesulfurdioxid converts the alumina into a comsulfur dioxid of the generalnature of sulfites. A large portion of the silica, which is released bythe breaking down of the'silidrated silicic acid. At the end ofthistreatment a large portion of the ore has been dissolved, leaving aninsoluble residue, which consists largely of silica. The solution isseparated from the insoluble residue by filtration.

solution to cause-precipitation of the alumina. This is accomplished byheating the solution to a temperature of about 55 C. and subjecting .itto moderate agitation. Steam is introduced for heating the solusult ofthis treatment is the evolution of sulfur dioxid gas from the solution.The alumina, which is released by .the desulfiting process, isprecipitated as aluminium hydrate. The precipitated aluminium hydrate isnot pure aluminium hydrate, but contains a small amount of sulfur dioxidcompounds of aluminium of the general nature of basic aluminium sulfiteor aluminium sulfite. This precipitate of aluminium hydrate with theaccompanying sulfur dioxid compounds iss'ometimes spoken of as basicaluminium sulfite. Therefore, when the expression aluminium hydrate isused in the speci that the precipitate defined thereby is notnecessarily pure aluminium hydrate but may contain sulfur dioxidcompounds of aluminium. During this desulfiting process, 'the solublesilica is largely precipitated as hydrous silica. The result of thedesulfiting treatment is, therefore, the precipitation from the solutionof aluminium hydrate, together' with hydrous silica, while the stablecompounds of the other elements remain .in solution.

ing process is separated from the solution by filtration, and theseparated precipitate, which consists of aluminium hydrate and hydroussilica, is resulfited by being again treated with sulfur dioxid andWater in a manner similar to the former treatment of the ore, but.however, with as little water as possible. -The aluminium hydrate isconverted by the excess of sulfur dioxid into the unstable compound ofaluminium oxid and sulfur dioxid which has the general cates, stays insolution probably as a by? The next step consists in desulfiting thefication and claims, it is to be understood tion, and it isagitatedby'stirring. The re- 'The precipitate obtained by the desulfitcharacterof aluminium sulfite. The precipitated hydrous silica is, however, forthe most part, not redissolved by the-sulfur dioxid, but remains as aninsoluble residue. The insoluble residue of hydrous silica is separatedfrom the solution containing the aluminium oxid and sulfur dioxid bymeans.

and the hydrate converted to the .oxid by the loss of water, and asbasicaluminium sulfite is readily decomposed by heat and converted intothe oxid with the loss of its sulfur content, the term alumina, as usedin the specification and. claims, is intended to include not only thepure dehydrated or dry aluminium oxid, but also the aluminium oxid whichis combined with water to form the aluminium hydrate, or hydratedaluminaand basic aluminium sulfite. As above pointed out, the alumina obtainedby this method may contain .a small amount of silica which wasredissolved during the 'resulfiting operation and precipitated with the'aluminium hydrate during the subseouent desulfiting operation. Theamount of silica present as an impurity in the alumina obtained asthe'final product varies with the character ofthe ore, the concentration of the solutions, etc. The term alumina as applied to the productobtained by this method is not to be understood as-restricted to purealumina, but as inclusive of more or less impure or crude alumina, suchas'alumina containing a small amount of silica. The term silica is usedin the claims as inclusive of silica (SiO silica hydrate, hydratedsilica, silicic acid and like compounds of silicon.

The foregoing description of the preferred method of obtaining aluminafrom aluminous ores of. the class described specifi cally sets forth theprecise method which has been practised. -The invention is notlimited-to this precise method hereinbefore described, as the invention'is of broader aspect. In the first place, the method is not limited touse in connection with any particular aluminous ore ormaterial. Themethod is, however, particularly applicable to making alumina from oreswhich lend themselves readily to the sulfiting process As the i withonly preliminary grinding. Nephelin syenite is one of these ores; othersare sodalite and certain kaolins; Themethod may also housed on othermaterials, such as ores, minerals or substanceswhich have been renderedsulfitable by preliminary treatment. All of these things are referred toherein as sulfitable materials.

The sulfitin' treatment may be 'carriedout bytreating t e ore with. apreviously prepared solution of sulfurous acid, or the ore may beagitated in a previously prepared sulfurous acid solution, the strengthof which is renewed bypassing sulfur'dioxid gas into the water. Thetreatment of the ore with the sulfur dioxidand Water is preferablycarried out at atmospheric pressure. This sulfiting treatment may,however, be carried out at higher pressures.

While in the preferred method of sulfi'ting the ore, water to an amountequal to three times the weight of the ore is used and in subsequentsulfiting operations only asmall amount of Waterjis used, the invention,in its broader aspects, is not limited to these proportions. Withcertain ores, it is preferred toheat the precipitate formed during thefirst desulfiting operation to a temperature of. about 120 C. for alength of time sufiicient to partially dehydrate the silica beforesubjecting this-precipitate to the sulfiting process. This partialdehydrating renders the silica less soluble.

While under ordinary circumstances, the single repetition of thesulfiting and desulfiting o'perations is sufficient, under somecircumstances-it is desirable to sulfite and desulfite more times inorder to obtain alumina or the highest purity.

By selecting suitable ores and by carrying but the method with that endin view, it is possible to obtain alumina substantially free fromsilica. With other ores, or in making products in which some silica isnot objectionable, severalper cent. of silica may be present as animpurity in the alumina.

The expression sulfur dioxid and water, as used in the specification andclaims, is intended to define any compound or mixture of sulfur dioxid(S0,) and water (H 0) whether in the compound expressed by the formula H80, (sulfurous acld) or not.

The, separation of the soluble sulfites from the insoluble residue afterthe sulfiting operations, has been referred to as a process offiltration, and for this purpose a filter,

centrifugal machine or other apparatus may be employed.

The desulfiting operation in the preferred embodiment is accomplished byheating and stirring the mixture. This is the preferred method ofdesulfiting by reason of its cheapncss and efficiency; This operationmay be accomplished at temperatures as low as 35 C. with vigorousagitation,

the sulfit'e solutions. This has substantiallythe same effect inremoving'the sulfur dioxid as heating. While under ordinary conditionsof plant equipment, the-employment of heat would probably bemosteconomical, underother conditions the employmentof vacuum might bepreferred. As, for example, where waste power was available whichotherwise-would not be used, it could .be employed to exhaust the vesselfor the purpose of throwing down the alumina. It is to be understoodthat it is withinthe contemplation of the invention to practice thedesulfiting operations by simply boilingthe sulfite solution, althoughit is preferred to rkeepthe temperature as low as-possible and to relyon,agitation because the latter is.

cheaper and because there is less liability of oxidizing the sulfites tosulfates, and less liability-of getting iron in. with the precipitate.The foregoing methods of desulfiting may bereferred to as physicalmethods of desulfiting, but the invention is not limited tothese-methods as the operation may be accomplished by chemical methods,such as by the use of certain chemical reagents which have a radical ofgreater afiinity than the aluminium for the sulfur dioxid. -Examples' ofsuch reagents are found in the salts of alkali,or alkaline earth metals,such as the hydrate, carbonate or sulfids which will form relativelystable, soluble salts with the sulfur dioxid, and so break down theunstable compound of aluminium oxid and sulfur dioxid and precipitatethealumina. It is desirable that the sulfur dioxid usedin the sulfitingoperations should be free from sulfur trioxid so that-noaluminiumsulfate shall be formed during the sulfiting-op'erations,pandthe entire aluminous con'tentof the-ore may be obtained. In thisconnection it is to be pointed= out that during the de sulfitingoperations, it is desirable that free access of air to the solution beprevented, and that the temperature be raised to a point just sufficientto precipitate the alumina as aluminium hydrate, 'so that the ferrouscompounds are not' oxidized to ferric compounds and the precipitate ispractically free from iron.

oil the SO, gas. Butthis is not preferred because it is liable to resultin partially oxidizing the sulfites to sulfates.

In practising this method of obtaining alumina commercially, variouseconomies are practised, and one which is not without effecting a savingworth while, contemplates the recovery and re-use of the sulfur dioxidwhich is removed duringthe desulfiting operations, Another feature ofthe present invention which contributes to reducing the expense ofpractising the process resides in the valuable by-products. The mostimportant-of these by-products are sodium sulfite,

sodium hydrate, sodium hypo-sulfite and sulfur, which. are produced fromthe solvent liquor used in the first sulfiting' operation and which maybe'repeatedly used until it has become sufliciently concentrated to beavailable in the manufacture of sodium hypo-sulfite and sulfur. .Anotherby-prodnot is the hydrous silica remaining after the second sulfit-ingoperation. .This has commercial value and its production decreases thecost of producing thealumina.

A feature of this method which is of importance is that the extremelyinexpensive nature of the process permits the treatment of' ores fromwhich only a portion of the alumina is recovered. For example, it iscommercially practical to treat o-res running 30 and 35% alumina withthis'process when only two-thirds of this alumina, or about 20% .of thetotal ore, is extracted. Much depends upon the ore; with ores lendingthemselves with greatest adaptability to the process, substantially allthe aluminium is extracted; with other more obdurate ores, the processis so inexpensive that even they are available for its use.

It is desired to emphasize the fact that the only reagentemployed inthesulfiting operations is an inexpensive one, namely, sulfur dlOXld, sothat the process 1s. capable of being practised at extraordinarily lowcost. Notonly is the process'cheap by reason of the inexpensiveness ofthis reagent, but also by reason of the simplicity and inexpensivenessof the heating, stirring and filtering operations employed.

WVhat is claimed'is;-'-

1. The metho'dof making alumina which consists in subjecting sulfitable,aluminous materials to a sulfiting oper'ation by the-action of sulfurdioxid and water to transform alumina content into" a, relativelyunstable.

soluble compound or compounds of alumina and sulfur dioxid, and indesulfiting' the solution to break down the unstable com ound orcompounds of alumina and sulfur ioxid to transform alumina content intoa relatively unstable soluble compound or compounds of alumina andsulfur dioxid, with which is present some dissolved silica, in

desulfiting the solution to break down the unstable compound orcompounds of alumina and sulfur dioxid and precipitate alumina andsilica from the solution, in resulfiti'ng the precipitate by the actionof sulfur dioxid and water to transform alumina into a relativelyunstable soluble compound or compounds of alumina and sulfur dioxidleaving silica undissolved, and in desulfiting the solution to breakdown the unstable compound or compounds of alumina and sulfur dioxid andprecipitate alumina from the solution, substantially as described.

3. The method of making alumina which consists in subjecting sulfitablealuminous and silicious materials to a sulfiting operation by the actionof sulfur dioxid and water to transform alumina content into arelatively' unstable soluble compound or compounds of alumina and sulfurdioxid, with which is present some dissolved silica, in desulfiting thesolution to break down the unstable compound or compounds of alumina andsulfur dioxid and precipitate alumina and silica from the solution, inresulfiting the precipitate bythe action of sulfur dioxid and a smallamount of water to transform alumina into a relatively unstable solublecompound or compounds of alumina and sulfur dioxid leaving substantiallyall of the silica undissolved, and in desulfiting the solution to' breakdown the unstable compound or compounds of alumina and sulfur dioxid andprecipitate alumina from the solution, substantially as described.

4. The method of making alumina which consists in subjecting sulfitablealuminous materials to a sulfiting operation wherein the materials inthe presence of water are acted upon by sulfur dioxid gas passed intothe mixture to transform alumina content into a relatively unstablesoluble compound or compounds of alumina and sulfur dioxid, and indesulfiting the solution to break down the unstable compound orcompounds of alumina and sulfur dioxid and precipitate alumina from thesolution, substantially as described.

5. The method of making alumina which. consists in subjecting sulfitablealuminous materials to a sulfiting operation by'the action of sulfurdioxid and water to transform alumina content into a relatively unstablesoluble compound or compounds of alumina and sulfur dioxid, and'indesulfiting the solution by heating it to break down the unstablecompound or compounds of alumina and sulfur dioxid and precipitatealumina from the solution,'substantially as described,

6. The method of making alumina. which consists in subjecting sulfitablealuminous materials to a sulfiting operation by the acdown the unstablecompound or compounds 7 of alumina and sulfur dioxid and precipitatealumina from the solution, substantially as described.

7 The method of making alumina which consists insub ecting sulfitablealuminous materials to a sulfiting operation by the vaction of sulfurdioxid and water to transform I alumina content. into a relativelyunstable soluble compound or compounds of alumina and sulfur dioxid, andin desulfiting the solution by heating to a temperature of about 55 C.and agitating it to break down the unstable compound or compounds ofalumina and sulfur dioxid and L precipitate alumina from the solution,substantially as described.

8. The method of making alumina which consists in subjecting sulfitablealuminous and silicious materials to a sulfiting' operation by theaction of sulfur dioxid and water to transform alumina content into arelatively unstable soluble compound or compounds of alumina and sulfurdioxid, with which .is present some dissolved silica, in filtering themass to remove insoluble residue, in desulfiting the solution by heatingand agitating it to break down the unstable compound or compounds ofalumina and sulfur dioxid and precipitate alumina and silica from thesolution, in filtering the mixture to remove the solution, in subjectingthe precipitate to a second sulfiting' operation by the action of sulfurdioxid and water to transform alumina into a relatively unstable solublecompound or compounds of alumina and sulfur dioxid leaving silicaundissolved, in filtering the mixture to remove the undissolved silica,in desulfiting thesolution by heating and agitating it to break down theunstable compound or compounds of alumina and sulfur dioxid andprecipitatealumina, from the solution, and in filtering the mixture toobtain the precipitated alumina, substantially as described.-

, 9. The method of making alumina which consists in subjectingsulfitable aluminous and silicious materials to a sulfiting operation bythe action of sulfur dioxid and water to transform alumina content intoa relatively unstable, soluble compound or compounds of alumina andsulfur dioxid, with which is present some dissolved silica, indesulfiting the solution to break down the unstable compound orcompounds of alumina and sulfur dioxid and precipitate alumina andsilica from the solution, in heating the precipitate to renderthe silicaless soluble, in resulfiting the precipitate by the action of sulfurdioxid and water to transform lu-. mina into a relatively unstable,soluble compound or compounds of alumina and sulfur dioxid, leavingsubstantially all of the silica undissolved, and in desulfiting thesolution to break down the unstable compound or compounds of alumina andsulfur dioxid and precipitate alumina from the solution,

substantially as described.

.10. The. method of making alumina which consists in subjectinsulfi'table aluminous and silicious materiai tion by the action ofsulfur dioxid and water to transform alumina content into a relativelyunstable, soluble compound or compounds of alumina and sulfur dioxid,with which is present some dissolved silica, in desulfiting the solutionto break down the unstable compound or compounds of alumina and sulfurdioxid and precipitate alumina and silica from-:the solution, in heatingthe precipitate to about 120 C. to render the silica less soluble, inresulfiting the precipitate by the action of sulfur dioxid and watertotransform alumina into -a relatively unstable, soluble compound orcompounds of alumina and sulfur dioxid', leaving substantially all ofthe silica .undissolved, and i in 'desulfiting the solution to breakdown. the unstable compound or compounds of alumina and sulfur dioxidand precipitate to a sulfiting opera alumina. from the solution,substantially as described.

11 The method of making aluminawhich consists in subjecting sulfitablealuminous materials to a sulfiting operation by theaction of sulfurdioxid and water to transform alumina content intoa relatively unstablesoluble compound or compounds of "soluble compound or compounds ofalumina and sulfur dioxid, and in desulfiting the solution by heat andexhaustion with agitation to break down the unstable compound orcompounds of alumina and sulfur dioxid and precipitate alumina from thesolut-ion,

as described. p HERBERT T. KALMUS. WALTER L. :SAVELL. Witnesses:

, GEo. H. SMYTHE,

Jnssm V. Connor.

substantially

